The 2D images, also called monoscopic images, are represented by pixels on an X-Y plane that is applied to the display screen of the display device. In contrast, the 3D images have a depth in the Z-axis direction in addition to the pixels on the X-Y plane applied to the screen of the display device.
The 3D images are presented to the viewers (users) by simultaneously playing back the left-view and right-view images to be viewed respectively by the left and right eyes so that a stereoscopic effect can be produced. The users would see, among the pixels constituting the 3D image, pixels having positive Z-axis coordinates in front of the display screen, and pixels having negative Z-axis coordinates behind the display screen.
It is preferable that an optical disc storing a 3D image has compatibility with a playback device that can play back only 2D images (hereinafter, such a playback device is referred to as “2D playback device”). This is because, otherwise, two types of discs for 3D and 2D images need to be produced so that the 2D playback device can play back the same content as that stored in a disc for 3D image. Such an arrangement will take a higher cost. It is accordingly necessary to provide an optical disc storing a 3D image that is played back as a 2D image by the 2D play back device, and as a 2D or 3D image by a play back device supporting both the 3D and 2D images (hereinafter, such a playback device is referred to as “2D/3D playback device”).
Patent Literature 1 identified below is one example of prior art documents describing technologies for ensuring the compatibility in playback between 2D and 3D images, with respect to optical discs storing 3D images.